The most common form of malignant disease, skin cancer, is strongly associated with exposure to solar ultraviolet (nearby) radiation 300-400nm; artificial light sources which also emit near UV radiation and lifestyles which involve increasing exposure to near UV seem to be related to increasing incidence of skin cancer and the less common but more lethal malignant melanoma. In the past the study of the biological effects of UV have focused on the actions of germicidal ultraviolet wavelenghts (200-300nm) which are essentially absent in the human environment. It appears that the biological actions of near UV may be different from the responses induced by germicidal UV. Because of its large impact on human health it is clear that a better understanding of the various biological actions of near UV is of importance. The production of cancer is closely related to genetically active agents. It is proposed to compare the genetic actions of near and germicidal UV using yeast and mammalian cells as model systems. The recent development of the tunable dye laser and other near UV sources will permit examination of wavelength dependence of complex genetic actions which do not occur in prokaryotes including mitotic recombination, gene conversion and chromosome shattering, as well as the production of simple mutations. DNA repair defective yeast strains will assist in comprehension of the initial injury, repair systems and the relation of repair to mutation following near UV exposure and how these factors relate to responses induced by germicidal UV irradiation.